AbstractID: 7542 Title: The effects of dose calculation accuracy on beam angle optimization
For a beam angle to be preferential to other angles, it has to contribute more to achieving the
treatment goal for the specific patient. Based on this notion, we introduced a new concept,
angular cost function (ACF), for selecting beam angles. It is defined as the difference (increase)
in the final cost function when the specific beam orientation is omitted from a set of beams. The
value of ACF therefore represents the impact of this angle in minimizing the overall cost
function. A scheme for selecting beam angles based on ACF was also developed and tested. To
obtain ACF, beam intensities must be optimized for all beams. The calculation can take 30-60
minutes. If terma instead of the full kernel of a pencil beam can be used for dose calculation in
the ACF calculation stage, we can reduce the time to about 5 minutes, making it practical for
automated beam angle selection. This study compares 1) the angular cost functions; 2) the beam
angles resulting from our beam selection criteria; and 3) the differences in plan quality using the
angles selected based on the ACFs obtained with full scatter dose calculation and with primary
only. It demonstrates that for beam angle optimization, simple 1D dose calculation is sufficient
for the clinical cases tested. Both approaches yield similar ACFs and the differences in the
resultant beam angles are small. Even if the selected angles are slightly different, the effects on
the quality of the plans were found to be insignificant.